1. Field of the Invention
The present invention relates to a demodulation circuit for CDMA mobile communications and a demodulation method therefor.
2. Description of the Related Art
Conventionally, the demodulation circuit for this type of mobile communications is provided with a path search portion and a RAKE synthesis/reception portion. The path search portion measures a delay profile, which represents signal power distribution with respect to signal delay time, based on received signals and selects those paths with a high signal power within the measured range to notify the RAKE synthesis/reception portion of the timings of the paths. The RAKE synthesis/reception portion performs de-spreading for each path based on the notified path timings and RAKE-synthesis to exploit path diversity effects.
Radio waves received in such mobile communications environments are subject to signal level variation including path generation and extinction and also subject to the variation in the arrival time of the path to the receiving end due to multipath fading, shadowing and so on. Under such large path variations, the reception qualities will degrade when a sudden level decrease or extinction of paths under search takes place. Therefore, a path search processing to select stable paths out of the arrived paths and assign the stable paths to the fingers is desired.